Mechanochemical synthesis of the Α-AlH₃/LiCl nano-composites by reaction of LiH and AlCl₃: Kinetics modeling and reaction mechanism

Mechanochemical activation-assisted synthesis, compared to conventional wet methods, exhibits advantages such as higher chemical homogeneity and better quality of the resulting nano-crystals, in preparing nano-sized aluminum hydride (AlH₃). Solid/liquid state milling is effective and convenient for production of α-AlH₃/LiCl nano-composites through a mechanochemical reaction of LiH and AlCl₃ in [2-Eim] OAc. However, the kinetics of this process has not been thoroughly studied. In this work, we studied the kinetics of mechanochemical synthesis of α-AlH₃/LiCl nano-composite to understand the reaction process and find the optimum milling parameters (including shortest time to achieve high-quality product). We performed isothermal desorption tests for as-milled samples at 80 °C. Structures of the products were analyzed using X-ray powder diffraction. Johnson-Mehl-Avrami (JMA) model was adopted to describe the process, which contains transformation fraction and chemical reaction controlled regime. Kinetics of mechanochemical reaction at the beginning was limited by diffusion rate of the reagent, and later controlled by nucleation of AlH₃. By fitting the experimental data, apparent activation energy for the mechanochemical reaction was calculated as 39.6 kJ/mol.